Laminating paper compound is a crucial post-printing step in offset printing for color boxes. The viscosity and pressure applied during this process directly influence the efficiency and quality of the final box. This technique is commonly used for multi-layer cartons (three-ply and five-ply), corrugated boxes, folding cartons, U/V coated tiles, tile-mounted cards, and double-layered cards under 500g. These products are widely used in packaging for beer, liquor, beverages, food, fruits, electronics, and cosmetics. Some small manufacturers purchase pre-printed color boards and mount them themselves, producing mooncake boxes in summer and fruit boxes in winter. Many beer breweries also opt for offset-printed veneer boxes. For example, Venus Beer once purchased three laminating machines at once.
Due to process limitations, the composite efficiency is relatively low, with a width range of 1200mm to 1600mm and a production speed of 2500 to 7000 sheets per hour. Therefore, the laminating process is more suitable for smaller batch productions with complex structures. Large-volume RSC boxes typically use flexographic printing after coloring, while dot printing may use either flexographic or gravure pre-printing. Product size restrictions depend on the equipment. From a technical standpoint, smaller boxes are easier to handle and maintain better quality. It's important to align the grain direction of the paper when performing multi-layer lamination. The grain directions of the two layers should be perpendicular to each other, and the grain direction of the box should be perpendicular to the flute direction of the corrugated board.
Automatic laminating machines require high-quality cardboard, smooth and dry surface paper, and experienced operators. To prevent the fluting from being crushed or damaged during lamination, the cardboard must not be too soft, and moisture content should stay below 14%. Additionally, the press pressure, angle, and speed must be carefully adjusted. Domestic veneer machines typically have an effective lamination length of 3.2 meters, but many factories request manufacturers to extend it to 3.8 meters. A longer pressing length allows operators to remove some pressure feed rollers as needed.
These machines are equipped with a hydraulic induction system at the pressing section, which automatically adjusts the drum height to accommodate different paper thicknesses. This feature reduces operator workload and protects the structural integrity of the boxes. Important physical properties like compression strength, flat crush resistance, bursting strength, and bonding strength are critical for corrugated boxes. These properties depend on the paper and board processing techniques, and proper bonding is essential for the final product.
The adhesion during lamination directly affects the next stage of box manufacturing and customer packaging. Gluing is a vital part of the process. If the adhesive is uneven, it can lead to blistering, poor adhesion, and visible glue marks on the back of the board. Rubber powder might even appear on the fluting. The precision of the laminating machine determines how evenly the glue is applied. The outer and inner rubber rolls must have consistent roundness, ensuring they don’t become eccentric over time. This ensures stable performance for at least five years. The fully self-reading head uses a built-in glue tank, a block-type pump, and applies glue through hydraulic pressure, resulting in even, safe, and hygienic application.
The glue used for mounting is usually starch-based or chemical glue. There are two types of starch glue: yellow glue and white glue. Yellow glue has largely been phased out in domestic applications. White glue is currently preferred due to its availability, environmental friendliness, affordability, and ease of use. However, it has weaker adhesion, tends to mold easily, dries slowly, and becomes brittle after drying.
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